Bug 806256 - Improve WrapPreserve3DList's behaviour by walking through nsDisplayWrapList without flushing the temp list. r=roc

layout/generic/nsFrame.cpp

@@ -1764,69 +1764,63 @@ DisplayDebugBorders(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
 #endif
 
 static nsresult
-WrapPreserve3DListInternal(nsIFrame* aFrame, nsDisplayListBuilder *aBuilder, nsDisplayList *aList, uint32_t& aIndex)
+WrapPreserve3DListInternal(nsIFrame* aFrame, nsDisplayListBuilder *aBuilder, nsDisplayList *aList, nsDisplayList *aOutput, uint32_t& aIndex, nsDisplayList* aTemp)
 {
   if (aIndex > nsDisplayTransform::INDEX_MAX) {
     return NS_OK;
   }
 
   nsresult rv = NS_OK;
-  nsDisplayList newList;
-  nsDisplayList temp;
   while (nsDisplayItem *item = aList->RemoveBottom()) {
     nsIFrame *childFrame = item->GetUnderlyingFrame();
 
     // We accumulate sequential items that aren't transforms into the 'temp' list
-    // and then flush this list into newList by wrapping the whole lot with a single
+    // and then flush this list into aOutput by wrapping the whole lot with a single
     // nsDisplayTransform.
 
     if (childFrame && (childFrame->GetParent()->Preserves3DChildren() || childFrame == aFrame)) {
       switch (item->GetType()) {
         case nsDisplayItem::TYPE_TRANSFORM: {
-          if (!temp.IsEmpty()) {
-            newList.AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, &temp, aIndex++));
+          if (!aTemp->IsEmpty()) {
+            aOutput->AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, aTemp, aIndex++));
           }
-          newList.AppendToTop(item);
+          aOutput->AppendToTop(item);
           break;
         }
         case nsDisplayItem::TYPE_WRAP_LIST: {
-          if (!temp.IsEmpty()) {
-            newList.AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, &temp, aIndex++));
-          }
           nsDisplayWrapList *list = static_cast<nsDisplayWrapList*>(item);
-          rv = WrapPreserve3DListInternal(aFrame, aBuilder, list->GetList(), aIndex);
-          newList.AppendToTop(list->GetList());
+          rv = WrapPreserve3DListInternal(aFrame, aBuilder, list->GetList(), aOutput, aIndex, aTemp);
           list->~nsDisplayWrapList();
           break;
         }
         case nsDisplayItem::TYPE_OPACITY: {
-          if (!temp.IsEmpty()) {
-            newList.AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, &temp, aIndex++));
+          if (!aTemp->IsEmpty()) {
+            aOutput->AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, aTemp, aIndex++));
           }
           nsDisplayOpacity *opacity = static_cast<nsDisplayOpacity*>(item);
-          rv = WrapPreserve3DListInternal(aFrame, aBuilder, opacity->GetList(), aIndex);
+          nsDisplayList output;
+          rv = WrapPreserve3DListInternal(aFrame, aBuilder, opacity->GetList(), &output, aIndex, aTemp);
+          if (!aTemp->IsEmpty()) {
+            output.AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, aTemp, aIndex++));
+          }
+          opacity->GetList()->AppendToTop(&output);
           opacity->UpdateBounds(aBuilder);
-          newList.AppendToTop(item);
+          aOutput->AppendToTop(item);
           break;
         }
         default: {
-          temp.AppendToTop(item);
+          aTemp->AppendToTop(item);
           break;
         }
       } 
     } else {
-      temp.AppendToTop(item);
+      aTemp->AppendToTop(item);
     }
  
     if (NS_FAILED(rv) || !item || aIndex > nsDisplayTransform::INDEX_MAX)
       return rv;
   }
     
-  if (!temp.IsEmpty()) {
-    newList.AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, &temp, aIndex++));
-  }
-
-  aList->AppendToTop(&newList);
   return NS_OK;
 }
 
@@ -1834,7 +1828,16 @@ static nsresult
 WrapPreserve3DList(nsIFrame* aFrame, nsDisplayListBuilder* aBuilder, nsDisplayList *aList)
 {
   uint32_t index = 0;
-  return WrapPreserve3DListInternal(aFrame, aBuilder, aList, index);
+  nsDisplayList temp;
+  nsDisplayList output;
+  nsresult rv = WrapPreserve3DListInternal(aFrame, aBuilder, aList, &output, index, &temp);
+
+  if (!temp.IsEmpty()) {
+    output.AppendToTop(new (aBuilder) nsDisplayTransform(aBuilder, aFrame, &temp, index++));
+  }
+
+  aList->AppendToTop(&output);
+  return rv;
 }
 
 nsresult